Beach Example 2 Flashcards
(26 cards)
Adaptive Antenna Definition
a multi-element antenna w/ a BF capable of adjusting / controlling the beam pattern of the antenna system in terms of main beam + null placement + sidelobe control
Benefits of cap, service (bit rate) + range enhancement from an adaptive antenna system? (4)
- Both SFIR + SDMA used to incr. network cap
- Single Antenna array system, impact of delay spread can also be reduced
- Higher data rate services offered for non-eq. systems
- Range extension can be obtained by aligning the array gain in the direction
Differences between fixed + fully adaptive BF? (2)
Fully Adapt. - full complex weights
Fixed - similar to the grid of beams / Aalborg Alg.
Why is transmit BF a problem in FDD systems?
UL + DL will experience freq. selective fading
—> exhibit different power azimuth spectrum
Adaptive Control Alg. (5)
(GMMOA)
Grid of Beams - GoB
Maximal Ratio Combining - MRC
Music Based Beam Synthesis - MUS
Optimum Combining - OPT
Aalborg Alg. - AUC
Grid of Beams (3)
- 13 fixed beams (10 degree intervals from -60 to 60 in azimuth) are synthesised by the BF
- Beam w/ highest o/p power is selected for reception
- Same look direction is used for the transmit case
Maximal Ratio Combining (2)
- performs maximum ratio combining on UL + uses same weight vector for DL
- Maximises SNR @ combiner by co-phasing the array signals + weighting them according to their SNR
Music Based Beam Synthesis
Super resolution DoA alg. is used to identify src locations and drive BF
Optimum Combining (2)
- Training codes are used as a reference signal to compute the Wiener optimum weight vector
- Minimising the error signal between the reference + weighted o/p array
Aalborg Alg. (2)
- 22 beams formed over 120 degrees
- Beam w/ highest correlation w/ the training seq is selected for both reception + Tx
Control Alg. used in large/small cell deployment
Large - Spatial Reference (DoA then BF)
Small - Optimum Combiner
Temporal Reference BF
appl of a training seq w/ a high correlation to the wanted signal
How does MIMO provide a capacity enhancement over conventional systems? (2)
- MIMO facilitates the stimulation + reslutions of multiple orthogonal spatial channels
- Channels can convery truly parallel info bearing waveforms @ same time + freq
- incr. info cap. compared to a SISO system
Property of MIMO channel for a cap. enhancement?
multipath richness leading to a full rank H matrix
Potential capacity gains from using MIMO? (3)
- scales linearly w/ # antennas for a square
- Assume IID Rayleigh channel
- e.g. 4x4 = x4 gain
Why are the gain of the eigenvalues important when assessing the cap of MIMO system?
eigen values specify the individual gains of the orthogonal spatial channels + their ability to carry info
Waterfilling definition (2)
- A practical MIMO channel will have different eigen channel gains
- Load high gain channels w/ more info
- i.e. waterfilling, greater capacity can be achieved
How is Waterfilling achieved? (3)
- Feedback used to access CSI
- Rx observes + feeds this back to Tx
- Tx adjusts mod + coding rates to match
How can # spatial channels be determined from the equipment config + channel parameters?
Max # spatial channels = min # of:
- Tx antennas
- Rx Antennas
- Scatters in environment
Why does the offered cap. of individual spatial channels vary in a practical deployment of a MIMO system? (2)
Offered cap. of a MIMO syst is lower due to:
- channel correlation
- lower eigen channel gains
Spatial Multiplexing definition (2)
- individual spatial channels carry a part of the message + recombine @ Rx
- sum cap. is sum of the individual orthogonal spatial channels
Space-Time Code Definition (3)
- Transmitted waveform is coded over both space + time = diversity
- Diversity reception can also be employed
- Provides robust transmission + no capacity expansion
Differences between Spatial Multiplexing + Space-Time Coding (2)
SM - provides throughput enhancement, but needs high SNR for signal separation
STC - provides good BER / outage performance @ low SNR
Massive MIMO defintion
A MIMO system w/ >50 . antennas @ AP / BS serving a multi-user MIMO network w/ 10 users
